The present invention relates to an audio input/output device designed to support operations of various audio device by means of a single audio jack, and a method for switching input/output functions of such an audio input/output device. The present invention is for example applicable to a small-sized portable information terminal.
The improvement of voice recognition techniques in recent years induces the need for a terminal having both a microphone input function to input voice and a speaker output function to feed back a voice recognition result to a user.
There has been proposed various solutions in relation to the input of voice, which require input from two microphones for accurate recognition of voice input in high-noise environment, namely, a microphone for collecting voice and a microphone for collecting surrounding noise. These solutions are believed to become more notable and useful in various occasions of using voice recognition.
In such solutions for voice recognition and occasions of using the same as described above, the terminal is required to have audio input/output functions realized by at least two microphones for input and at least one speaker for output.
When the solution is employed in a laptop computer having a physically large size, for example, it is possible to mount therein interfaces and circuits for respective input/output functions including, for example, stereo headphone output and stereo microphone input.
Such conventional technique is disclosed, for example, in Japanese Laid-Open Patent Publication Nos. 2001-195100 and 2002-8798.
However, according to the conventional techniques, it is physically difficult to mount a plurality of jack interfaces in small-sized portable information terminals represented by PDA or the like. An information terminal such as PDA typically has a single interface for a headphone, or an earphone microphone.
In order to realize accurate voice recognition in high-noise environment, the information terminal is required to have a plurality of audio jack interfaces having a microphone input function for collecting voice, a microphone input function for collecting surrounding noise, and a speaker output function for feeding back a voice recognition result to the user. This induces a problem of increase in the size of the terminal. In order to solve the problem relating to the terminal size, operations of various audio devices must be supported by a single audio jack.
In this case, the audio interface of the information terminal must be supplied with electrical signals from four different pins including GND (ground) pin. The input/output functions as described above can be realized by employing a 4-pin audio jack which has already been commercialized.
However, even for a small-sized information terminal provided with this type of 4-pin audio jack, it is necessary to assume that the information terminal is connected to other equipment than a headset which is used for accurate voice recognition in high-noise environment, such as a regular 3-pin audio device or a 4-pin audio device having a special signal. It is also necessary to prevent the basic voice input/output functions from being damaged.
The environment in which the headset for realizing accurate voice recognition in high-noise environment is used is obviously high-noise environment. Therefore, when the headset is used with a same output volume as that for a regular audio device, the surrounding noise sometimes makes it difficult for the user to hear the sound no matter how near the sound source is. Additionally, the user is required to manually change the setting of sound output volume between when using the headset and when using a regular audio device. This poses a problem to the user because such manual operation is troublesome.